1. Field of the Invention
The invention relates to a display, and more particularly, to a display capable of compensating for luminance of an environment.
2. Description of the Prior Art
Almost all electronic devices need to transfer information through a display device. A computer system, for example, needs a display to show the execution condition of application software to users. A cell phone also needs a display to show communication data to users. These products are commonly found in consumers' homes because of the rapid progress of communications technology. Moreover, said display devices have progressed from old-fashioned cathode ray tube (CRT) displays to LCDs and plasma displays.
Please refer to FIG. 1 , which is a diagram of a γ=2.2 characteristic curve of a CRT display and a γ=1/2.2 characteristic curve of a video recording device according to the prior art. As is well known in the art, the relationship between red-green-blue (RGB) gain values and outputting luminance for human vision complies with the γ=2.2 characteristic curve shown in FIG. 1, due to characteristics of CRT displays (such as the response time of the cathode ray tube). In addition, in the past, all displays were CRT displays. Therefore, corresponding video recording devices should have an inverse γ=1/2.2 characteristic curve. For the user, the visual effect can be a linear γ=1 curve (as the dotted line shown in FIG. 1). This makes the image shown on the display resemble the real world.
Although LCDs and plasma displays are available on the market, video recording devices still have the γ=1/2.2 characteristic curve. Therefore, said LCD and plasma displays have to comply with the γ=2.2 characteristic curve to give users a ‘real world’ effect.
In general, a normal LCD includes an ambient sensor to control the luminance of the backlight module to make the luminance correspond to the luminance of the environment. In other words, if the luminance of the environment becomes lighter or darker, the image shown on the display will also be adjusted. This is so users will not feel the effect of an environment change.
Unfortunately, the above-mentioned adjustment method suffers from two problems. Please refer to FIG. 2, which is a diagram of characteristic curves of an LCD. If the luminance of the backlight module is directly adjusted, the RGB gain values cannot be adjusted perfectly according to the γ=2.2 characteristic curve. In other words, when the luminance of the backlight module changes, because the RGB gain values change, the proportions of the RGB colors of the processed image signal will also change in accordance with the variances of the RGB gain values. This introduces distortions to the image. As shown in FIG. 2, if the luminance of the backlight module is adjusted to be stronger, the characteristic curve may be shifted from the original γ=2.2 curve to a curve having a lower curvature (for example, γ=1.2). On the other hand, if the luminance of the backlight module is adjusted to be darker, the characteristic curve may be shifted from the original γ=2.2 curve to a curve having a higher curvature (for example, γ=3.2). These shifts result in a displayed image that is significantly different from the original γ=2.2 curve, and will therefore have unclear details; the exposure of the entire image will be too great (meaning that the image is too light), or the exposure will not be sufficient (meaning that the image is too dark.)